Visible-light Photocatalytic H2 Production Research Articles

Enhanced visible-light photocatalytic H2 production of hierarchical g-C3N4 hexagon by one-step self-assembly strategy

Herein, self-assembly of hierarchical multihole g-C3N4 hexagon with excellent specific surface area (129 m2/g) and nitrogen vacancies were accomplished via a one-step polymerization of hydrothermal-treated dicyandiamide and ethylene-diamine-tetra-acetic acid (EDTA). The special chelate structure of EDTA efficiently enlarged a broad visible light response range, and the concentrations of EDTA promoted the self-assembly formation of different surface morphology. The photocatalytic H2 production rate under visible light for the optimal g-C3N4 hexagon (CN-20E) reaches 5839 μmol·g−1·h−1 and its apparent quantum efficiency reaches up to 7.3% at 420 nm, which has a 102 times higher for H2 production rate than that of bulk g-C3N4 (57 μmol·g−1·h−1). Special structure of the multihole hexagon endows them with remarkably visible light absorption, fast separation of photo-induced charge carriers, large surface areas as well as the exposure of potential photocatalytic active sites, thereby dramatically improved the H2 production property. Moreover, the forming process for the specific structure and the reaction mechanism of the enhanced photocatalytic activity were proposed according to the experimental results and theoretical calculations. This work exhibits a new avenue to rehandle graphitic carbon nitride precursor to build a grafted structure for developing highly efficient g-C3N4 in the practical photocatalytic application.

Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution

The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 µmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.

Atomically Dispersed Single Co Sites in Zeolitic Imidazole Frameworks Promoting High-Efficiency Visible-Light-Driven Hydrogen Production.

As photocatalysis technology could transform renewable and clean solar energy into green hydrogen (H2 ) energy through solar water splitting, it is regarded as the "Holy Grail" in chemistry field in the 21st century. Unfortunately, the bottleneck of this technique still lies in the exploration of highly active, cost-effective, and robust photocatalysts. This work reports the design and synthesis of a novel zeolitic imidazole framework (ZIF) coupled Zn0.8 Cd0.2 S hetero-structured photocatalyst for high-performance visible-light-induced H2 production. State-of-the-art characterizations and theoretical computations disclose that the interfacial electronic interaction between ZIF and Zn0.8 Cd0.2 S, the high distribution of Zn0.8 Cd0.2 S on ZIF, and the atomically dispersed coordinately unsaturated Co sites in ZIF synergistically arouse the significantly improved visible-light photocatalytic H2 production performance.

TiO2 nanosheets with exposed {001} facets co-modified by AgxAu1−x NPs and 3D ZnIn2S4 microsphere for enhanced visible light absorption and photocatalytic H2 production

A novel AgxAu1−x/ZnIn2S4/TiO2 photocatalyst with high photoactivity under visible light illumination is designed in this work, in which ZnIn2S4 displays a 3D flower-like microsphere structure, while TiO2 nanosheets with highly active {001} facets (TiO2 NS) are tightly embedded in the interspaces of ZnIn2S4 microspheres, and AgxAu1-x nanoparticles (NPs) are loaded on its surface, respectively. The exquisite design of AgxAu1−x/ZnIn2S4/TiO2 makes it possess remarkable superiority in photocatalysis. Firstly, by the dual modification of ZnIn2S4 and AgxAu1−x, the AgxAu1−x/ZnIn2S4/TiO2 displays a strong absorption in visible light region, and their absorption region can be modulated by changing the ratio of Ag and Au in AgxAu1-x nanoparticles due to the plasmon coupling effect of Ag and Au. Secondly, the high separation and transfer efficiency of photogenerated carriers is achieved in AgxAu1-x/ZnIn2S4/TiO2 by utilizing TiO2 as the electron transfer intermediary of ZnIn2S4 and AgxAu1−x. All of these make AgxAu1−x/ZnIn2S4/TiO2 exhibit an evident enhancement in the photocatalytic activity of H2 production. Significantly, the hydrogen production amount and rate of Ag0.2Au0.8/ZnIn2S4/TiO2 with 60 wt% ZIS after 10 h are 9862 μmol/g and 986.2 μmol/g/h, which is around 2098 times of pristine TiO2. The apparent quantum yield of Ag0.2Au0.8/ZnIn2S4/TiO2 after 10 h is about 1.47%. Moreover, the cycling test reveals that AgxAu1−x/ZnIn2S4/TiO2 shows the high stability in photocatalytic water spitting. Based on the characterization and photocatalytic results, the proposed photocatalytic mechanism is proposed.

In-situ creating elastic lattice O O bonds over semicrystalline yellow TiO2 nanoparticles for significantly enhanced photocatalytic H2 production

Atomic defects (e.g., Ti3+, oxygen vacancies) have been intenstively investigated for modifying TiO2 in order to reach visible light active photocatalytic H2 production. However, the atomic defects within TiO2 could easily act as photo-generated charge-carrier recombination centers, resulting in relatively low H2 conversion efficiency. In this paper, semicrystalline yellow TiO2 nanoparticles rich of superoxide ions are new synthesized by a simple aqueous solution method. Instead of introducing atomic defects, we show for the first time that catalytic performance can also be significantly improved via in-situ creating lattice OO bonds within metastable semicrystalline TiO2. The synthesized semicrystalline yellow TiO2 exhibits significantly enhanced photocatalytic activity for H2 production after cycle tests. The formaldehyde in aqueous solution is used as target pollutant to simulate industrial wastewater. In-situ created elastic lattice OO bonds are proposed to improve catalytic performance through facilitating the breakage of CH bonds of HCHO. A series of internally consistent reaction equations is proposed that describes the role of in-situ created lattice OO bonds for improving the catalytic performance. This is strongly supported by that the H2 production rate at the end of the fourth cycle test is significantly more than that of the beginning of the first cycle test.

A stable Ta3N5@PANI core-shell photocatalyst: Shell thickness effect, high-efficient photocatalytic performance and enhanced mechanism

Ta3N5 is a very promising visible-light-driven photocatalyst for water splitting and organic degradation. However, the low photocatalytic activity and poor photostability limit its application. To enhance the photocatalytic performance of Ta3N5, we prepared core-shell Ta3N5@polyaniline (PANI) by a chemisorption process. The effect of PANI content on the microstructure, optical, photoelectrochemical property and the photocatalytic activity of the samples were studied. The results showed that after the adsorption process, PANI was successfully coated on Ta3N5 with intimate contact and could significantly enhance the photocatalytic performance. The PANI shell thickness dramatically affected the photocatalytic activity. The Ta3N5@PANI 2 (PANI shell thickness: 0.9 nm) possessed the highest visible light photocatalytic H2 production rate of 72.6 μmol g−1 h−1 and RhB degradation rate of 0.041 min−1, which were 3.2 and 16.6 times higher than those of Ta3N5. The Ta3N5@PANI exhibited excellent photostability and reusability. The superior photocatalytic performance of the Ta3N5@PANI was attributed to the synergic effect, including the intense interfacial interaction, enhanced visible light absorption, efficient charge separation and corrosive holes transfer from Ta3N5 to PANI. Furthermore, DFT calculations were applied to explore the interfacial interaction between PANI and Ta3N5. This study suggests that PANI modification can improve the photocatalytic application of Ta3N5 for H2 production and RhB degradation.

Facile synthesis of rod-like g-C3N4 by decorating Mo2C co-catalyst for enhanced visible-light photocatalytic activity

Designing and optimizing visible-light-driven photocatalyst with cost-efficiency and high performance is very imperative and highly challenging for photocatalytic hydrogen evolution reaction. Herein, g-C3N4/Mo2C hybrid photocatalyst with one dimensional (1D) heterostructure for highly enhanced photocatalytic H2 generation activity were obtained by a facile two step processing, in which Mo2C nanoparticles were highly dispersed on rod-like g-C3N4 surface. Attributed to the synergistic effect of 1D structure and Mo2C co-catalyst, the resultant g-C3N4/Mo2C sample exhibits an impressive visible-light photocatalytic H2 production rate of up to 507 μmol·h−1·g−1 and quantum efficiencies of 3.74% at 420 nm, which is 9.8 times higher than that of bulk g-C3N4, indicating that decorating Mo2C as co-catalysts on the surface of g-C3N4 leads to the improved visible light absorption, promoted charge separation and enhanced the following H2-evolution rate. Moreover, the mechanism for the photocatalytic activity enhancement was also discussed. This study provides a guide for researchers to design efficient g-C3N4-based hybrid photocatalysts with excellent stability and photocatalytic activity during the photoreaction process.

A New and stable Mo-Mo2C modified g-C3N4 photocatalyst for efficient visible light photocatalytic H2 production

Design and preparation of highly efficient and stable cocatalysts are critical to the improvement of photocatalyst performance. A traditional cocatalyst consists of metal nanoparticles for the separation of photo-induced electron-hole pairs and for the reduction of protons. In this research we report a metal-semiconductor composite cocatalyst to increase light adsorption and to effectively enhance proton reduction capacity. A molybdenum rich molybdenum carbide (Mo-Mo2C) based noble-metal-free metal/semiconductor cocatalyst was loaded onto graphitic carbon nitride (g-C3N4) for highly efficient photocatalytic H2 evolution from water. The Mo-Mo2C was synthesized via a temperature-programmed reaction using (NH4)6Mo7O24·4H2O as a precursor. The cocatalyst loaded 2.0 wt.% Mo-Mo2C/g-C3N4 composite photocatalyst has demonstrated excellent photocatalytic performance. The hydrogen evolution rate for the 2.0 wt.% Mo-Mo2C/g-C3N4 nanocomposites can be as high as 219.7 μmol h−1 g−1, which is 440 times higher than that of g-C3N4 alone and 90% as high as 0.5 wt.% Pt/g-C3N4 photocatalyst (244.1 μmol h−1 g−1). Due to strong synergetic effects between Mo and Mo2C nanoparticles, this rate is 11.47 and 3.60 times higher than those for 2.0 wt.% Mo/g-C3N4 (19.1 μmol h−1 g−1) and 2.0 wt.% Mo2C/g-C3N4 (60.9 μmol h−1 g−1) photocatalysts respectively. Moreover, the 2.0 wt.% Mo-Mo2C/g-C3N4 catalyst is significantly stable for application in photocatalytic hydrogen evolution, with an apparent quantum efficiency of 8.3%—one of the highest noble-metal-free efficiencies reported in literature. All results indicate that metal/semiconductor composites can serve as highly efficient cocatalysts for photocatalytic hydrogen evolution from water reduction.

A ternary Z-scheme WO3–Pt–CdS composite for improved visible-light photocatalytic H2 production activity

Fabrication of advanced semiconductor system for photocatalytic water splitting into valuable hydrogen energy has attracted a lot of attention worldwide due to the increasing global energy crises. In this work, a ternary WO3–Pt–CdS composite was synthesized through coprecipitation and hydrothermal reactions. The ternary composite (i.e. WO3–Pt–CdS) showed a high hydrogen evolution rate of 390 μmol h−1 g−1 exceeding CdS alone (27 μmol h−1 g−1), WO3–CdS (55 μmol h−1 g−1), and CdS–Pt (135 μmol h−1 g−1). The enhanced photocatalytic activity is mainly attributed to the formation of Z-scheme heterojunction between WO3 and CdS, which results in the effective space charge separation. Meanwhile, the Pt in the as-prepared WO3–Pt–CdS plays an essential role as a bridge for accelerating the charge transportation between WO3 and CdS. This work provides another effective way of developing visible-light-driven photocatalysts for practical application.

2D/2D g-C3N4/MgFe MMO nanosheet heterojunctions with enhanced visible-light photocatalytic H2 production

As an emerging p-conjugated materials, graphitic carbon nitride (g-C3N4) has captured worldwide attention due to impending energy crisis and increasingly serious environmental contamination. In this work, the two-dimensional (2D) MgFe mixed metal oxide (MMO) derived from the layered double hydroxides precursor was employed to construct 2D/2D nanosheet heterojunction with g-C3N4. The formed CN/MgFe-30 nanosheet heterojunctions exhibited the optimal photocatalytic hydrogen production about 6.64 times (1.26 mmol/g−1·h−1) than that of pure g-C3N4 under the visible light irradiation, which were attributed to unique inter-plane 2D/2D structure and excellent synergistic effect between g-C3N4 and MgFe MMO. The experiment characterization proved that MgFe MMO nanosheet not only suppressed the overgrowth of g-C3N4, resulting in the formation of nanoscale g-C3N4, but also facilitated the photoinduced carrier separation and transfer based on 2D/2D CN/MgFe-X nanosheet heterojunctions. This proposed synthesis strategy pave a way to realize the large-scale production of nano-g-C3N4 based 2D/2D nanosheet heterojunctions photocatalysts for hydrogen production.

Hierarchical Honeycomb Br-, N-Codoped TiO2 with Enhanced Visible-Light Photocatalytic H2 Production.

The halogen elements modification strategy of TiO2 encounters a bottleneck in visible-light H2 production. Herein, we have for the first time reported a hierarchical honeycomb Br-, N-codoped anatase TiO2 catalyst (HM-Br,N/TiO2) with enhanced visible-light photocatalytic H2 production. During the synthesizing process, large amounts of meso-macroporous channels and TiO2 nanosheets were fabricated in massive TiO2 automatically, constructing the hierarchical honeycomb structure with large specific surface area (464 m2 g-1). cetyl trimethylammonium bromide and melamine played a key role in constructing the meso-macroporous channels. Additionally, HM-Br,N/TiO2 showed a high visible-light H2 production rate of 2247 μmol h-1 g-1, which is far more higher than single Br- or N-doped TiO2 (0 or 63 μmol h-1 g-1, respectively), thereby demonstrating the excellent synergistic effects of Br and N elements in H2 evolution. In HM-Br,N/TiO2 catalytic system, the codoped Br-N atoms could reduce the band gap of TiO2 to 2.88 eV and the holes on acceptor levels (N acceptor) can passivate the electrons on donor levels (Br donor), thereby preventing charge carriers recombination significantly. Furthermore, the proposed HM-Br,N/TiO2 fabrication strategy had a wide range of choices for N source (e.g., melamine, urea, and dicyandiamide) and it can be applied to other TiO2 materials (e.g., P25) as well, thereby implying its great potential application in visible-light H2 production. Finally, on the basis of experimental results, a possible photocatalytic H2 production mechanism for HM-Br,N/TiO2 was proposed.

Metal-Free 2D/2D Phosphorene/g-C3 N4 Van der Waals Heterojunction for Highly Enhanced Visible-Light Photocatalytic H2 Production.

The generation of green hydrogen (H2 ) energy using sunlight is of great significance to solve the worldwide energy and environmental issues. Particularly, photocatalytic H2 production is a highly promising strategy for solar-to-H2 conversion. Recently, various heterostructured photocatalysts with high efficiency and good stability have been fabricated. Among them, 2D/2D van der Waals (VDW) heterojunctions have received tremendous attention, since this architecture can promote the interfacial charge separation and transfer and provide massive reactive centers. On the other hand, currently, most photocatalysts are composed of metal elements with high cost, limited reserves, and hazardous environmental impact. Hence, the development of metal-free photocatalysts is desirable. Here, a novel 2D/2D VDW heterostructure of metal-free phosphorene/graphitic carbon nitride (g-C3 N4 ) is fabricated. The phosphorene/g-C3 N4 nanocomposite shows an enhanced visible-light photocatalytic H2 production activity of 571 µmol h-1 g-1 in 18 v% lactic acid aqueous solution. This improved performance arises from the intimate electronic coupling at the 2D/2D interface, corroborated by the advanced characterizations techniques, e.g., synchrotron-based X-ray absorption near-edge structure, and theoretical calculations. This work not only reports a new metal-free phosphorene/g-C3 N4 photocatalyst but also sheds lights on the design and fabrication of 2D/2D VDW heterojunction for applications in catalysis, electronics, and optoelectronics.

Hybridizing MoS2 and C60 via a van der Waals heterostructure toward synergistically enhanced visible light photocatalytic hydrogen production activity

Molybdenum disulfide (MoS2) as a representative transition-metal dichalcogenide (TMD) has been extensively used as a noble-metal-free cocatalyst for photocatalytic hydrogen (H2) production, but suffers from poor photocatalytic activity due to the catalytic inactivity of its basal plane. Herein, by bounding another metal-free cocatalyst, C60, with MoS2, we report the first MoS2-C60 hybrid featuring a van der Waals heterostructure prepared via a facile and eco-friendly solid-state mechanochemical route. C60 bounding onto the edge of MoS2 nanosheets leads to the decreases of both the number of layers and the size of MoS2 nanosheets, as well as a negative shift of the conduction band minimum along with a positive shift of valance band maximum relative to the bulk MoS2 and MoS2 ball-milled without C60 (MoS2-BM). Under the optimized weight ratio of MoS2:C60 (1:1) in the raw mixture subject to ball-milling, MoS2-C60 hybrid containing 2.8 wt% C60 shows an exceptional visible light photocatalytic H2 production rate of 6.89 mmol h−1 g−1 in the presence of a photosensitizer Eosin Y (EY), which is significantly enhanced relative to the bulk MoS2 and pristine C60, both of which show almost no photocatalytic H2 activity. Thus, the synergistic enhancement of photocatalytic activities of both MoS2 and C60 is revealed.

Promoting Charge Separation in g-C3N4/Graphene/MoS2 Photocatalysts by Two-Dimensional Nanojunction for Enhanced Photocatalytic H2 Production

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for solar H2 generation, but the practical application of g-C3N4 is still limited by the low separation efficiency of photogenerated charge carriers. Herein, we report the construction of ternary g-C3N4/graphene/MoS2 two-dimensional nanojunction photocatalysts for enhanced visible light photocatalytic H2 production from water. As demonstrated by photoluminescence and transient photocurrent studies, the intimate two-dimensional nanojuction can efficiently accelerate the charge transfer, resulting in the high photocatalytic activity. The g-C3N4/graphene/MoS2 composite with 0.5% graphene and 1.2% MoS2 achieves a high H2 evolution rate of 317 μmol h–1 g–1, and the apparent quantum yield reaches 3.4% at 420 nm. More importantly, the ternary g-C3N4/graphene/MoS2 two-dimensional nanojunction photocatalyst exhibits much higher photocatalytic activity than the optimized Pt-loaded g-C3N4 photocatalyst.

One-dimensional Au/SiC heterojunction nanocomposites with enhanced photocatalytic and photoelectrochemical performances: Kinetics and mechanism insights

In this work, highly dispersed Au nanoparticles (NPs) decorated SiC nanowires (NWs) hybrids were firstly synthesized by a facile deposition-precipitation method. The as-prepared Au/SiC samples were characterized using various instrumental methods such as XRD, TEM, EDS, UV–vis DRS, BET, FTIR, XPS, PL, TRPL, and photoelectronchemical measurements. The solar H2 production performances were investigated by using Na2S as sacrificial reagents in water under simulated sunlight illumination produced from a 300 W xenon lamp. Results showed that a significantly enhanced photoactivity for H2 evolution (1495.8 μmol h−1·g−1) with apparent quantum efficiency (AQE) of 2.12% was achieved over the compostion-optimized Au/SiC composite (with 0.5 wt% Au), which was much higher than those of pure SiC NWs, Pt NPs deposited SiC NWs sample as well as the previously reported SiC-based catalysts. In cyclic tests, the AS0.5 showed acceptable photocatalytic stability and good structural stability. PL, TRPL and photoelectrochemical measurements disclosed that improved charge separation and retarded charge recombination were realized. However, the Au-loaded SiC products with strong surface plasmon resonance (SPR) absorption showed no activity for visible light photocatalytic H2 production (λ ≥ 400 nm). Based on band-gap structures, the critical factors for SPR effect of Au NPs in activating or enhancing the visible-light photoactivities of semiconductors were proposed. This work can pave the avenue to the development of plasmonic metal decorated other narrow band gap semiconductors with plasmon-enhanced visible-light photoactivity for solar water splitting and related applications.

Defect-rich O-incorporated 1T-MoS2 nanosheets for remarkably enhanced visible-light photocatalytic H2 evolution over CdS: The impact of enriched defects

Structure and phase engineering in low-cost and earth-abundant MoS2 materials have been widely explored in catalytic domains. Designing MoS2 nanostructures associated with the number of catalytically active edge sites is of particular importance for obtaining an effective HER photocatalytic system. We herein report hydrothermal-synthesized defect-rich O-incorporated 1T-MoS2 nanosheets (denoted as DRM), and their implementation as cocatalysts to form photocatalytic heterostructure with CdS nanorods (denoted as DRM-C). For comparison, defect-free O-incorporated 1T-MoS2 nanosheets (denoted as DFM) and corresponding heterostructure i.e. DFM-C were simultaneously synthesized. A carefully comparative study on DRM and DFM demonstrates that the DRM cocatalyst exhibits more abundant defects in the basal planes and edges, and thus leading to the higher density of active sites beneficial to the photocatalytic HER. As a result, the optimized 20 wt% DRM-C exhibits an extraordinary visible-light (λ > 420 nm) photocatalytic H2 production rate of 132.4 mmol h−1 g−1, obviously higher than that of 20 wt% DFM-C (102.1 mmol h−1 g−1). Interestingly, such an impressive activity of 20 wt% DRM-C is demonstrated to be superior to that of pure CdS (20.0 mmol h−1 g−1) and conventional Pt/CdS (89.0 mmol h−1 g−1). To the best of our knowledge, this DRM-C photocatalyst shows the advanced visible-light-driven HER performance among reported MoS2/CdS composites.

Remarkable positive effect of Cd(OH)2 on CdS semiconductor for visible-light photocatalytic H2 production

In the past decade, photocatalytic H2 production over CdS semiconductor has garnered considerable interest due to its visible-light response, suitable band structure, and controllable morphologies. To pursue higher photocatalytic efficiency and more feasibility for practical industrial applications, Cd(OH)2 nanoparticle decorated CdS rod composites were designed and successfully fabricated in this study by a facile one-step hydrothermal method in strong alkali NaOH solution. The synthesis process followed a “mother liquor circulation” criteria since no NaOH was lost during the whole preparation course, which could greatly save costs and be conducive to the realization of large-scale production. When the content of Cd(OH)2 was 17.6 mol% in the obtained composite, the photocatalytic H2 production rate reached the highest (579.0 μmol h−1) with the help of 0.6 wt% platinum (Pt), which was more than 386 and 15 times higher than that of Pt/Cd(OH)2 and Pt/CdS, respectively. It was evidenced that such surprising and prominent enhancement of photoactivity was mainly attributed to the presence of Cd0 as an electron transport intermediary, which was produced by in-situ photoreduction of Cd(OH)2 interfacial layer between CdS and Pt. This work could not only highlight the significant roles of Cd(OH)2 on invigorating the photoactivity of CdS for H2 production, but also open an avenue of using the concept of mother liquor circulation in the photocatalyst synthesis process to satisfy the industrial manufacture requirement.

Zn-vacancy mediated electron-hole separation in ZnS/g-C3N4 heterojunction for efficient visible-light photocatalytic hydrogen production

Vacancy defects play an important role in modifying the electronic structure and the properties of photoexcited charge carriers by introducing additional energy levels and consequently enhanced the photocatalytic activity of photocatalyst. In this work, we report a ZnS/g-C3N4 heterostructure with abundant zinc vacancy defects on the surface of ZnS to emphasis the synergistic promotion on charge separation. The ZnS/g-C3N4 heterostructured photocatalyst possesses low over-potential, extended absorption in the visible light region, and promoted photoinduced electron-hole separation capability. Fluorescence emission spectra and XPS results confirm that existence of abundant zinc vacancies on ZnS. VZn-rich CZV20 (g-C3N4/ZnS-20 wt%) heterojunction exhibits more than 30 times higher photocatalytic H2 evolution rate (713.68 μmol h−1 g−1) than that of pure g-C3N4 (24.09 μmol h−1 g−1) under visible light irradiation and high stability during the prolonged photocatalytic operation. The enhanced photocatalytic performance can be attributed to the intimate interfacial contact between g-C3N4 and ZnS nanoparticles, increasing the light-absorbing capacity and charge separation efficiency of ZnS/g-C3N4 heterojunction. And more importantly, the visible-light photocatalytic H2 production activity can be ascribed to the two-photo excitation in the middle band gap of ZnS. This work demonstrates that appropriate Zn vacancy defects modified ZnS/g-C3N4 heterojunction can be used for highly efficient visible-light photocatalysis.

High light harvesting efficiency CuInS2 quantum dots/TiO2/MoS2 photocatalysts for enhanced visible light photocatalytic H2 production.

Expanding the photoresponse range of TiO2-based photocatalysts is of great interest for photocatalytic H2 production. Herein, noble-metal-free CuInS2 quantum dots were employed as a novel inorganic dye to expand the visible light absorption of TiO2/MoS2 for solar H2 generation. The as-prepared CuInS2/TiO2/MoS2 photocatalysts exhibit broad absorption from the ultraviolet to near-infrared region. Under visible light irradiation (λ > 420 nm), the CuInS2/TiO2/MoS2 photocatalyst with 0.6 mmol g-1 CuInS2 and 0.5 wt% MoS2 showed the highest H2 evolution rate with a value of 1034 μmol h-1 g-1. Moreover, a considerable H2 evolution rate of 141 μmol h-1 g-1 was obtained under the irradiation of the optimized CuInS2/TiO2/MoS2 photocatalyst with >500 nm light. The reaction mechanism of the CuInS2/TiO2/MoS2 photocatalyst for photocatalytic H2 evolution was investigated in detail by photoluminescence decay study, and the results showed that the photoexcited electrons of CuInS2 can be transferred efficiently through TiO2 to MoS2 and then react with the absorbed protons to generate H2. The reported sensitization strategy tremendously improves the visible light absorption capacity and the photocatalytic performance of TiO2-based photocatalysts.

Constructing a ZnIn2S4 nanoparticle/MoS2-RGO nanosheet 0D/2D heterojunction for significantly enhanced visible-light photocatalytic H2 production.

A zero-dimensional (0D)/two-dimensional (2D) heterojunction has an excellent advantage of boosting the photo-generated carrier separation and obtaining enhanced photocatalytic activities. Here, a ZnIn2S4 nanoparticle/MoS2-RGO nanosheet 0D/2D heterojunction was prepared by a rapid and low temperature hydrothermal method. TEM characterization results reveal that ZnIn2S4 nanoparticles are uniformly dispersed on the surface of MoS2-RGO nanosheets, which can provide abundant active sites and shorten the charge-migration distance, while the MoS2-RGO nanosheet acts as a support to avoid the aggregation of 0D ZnIn2S4 nanoparticles and also serves as a low-cost cocatalyst for effective hydrogen evolution. Through optimizing the MoS2-RGO composition and content, the highest hydrogen evolution rate of 425.1 μmol g-1 h-1 was obtained over the ZnIn2S4/MoS2-RGO 0D/2D heterojunction photocatalyst under visible light irradiation (λ > 420 nm), which is about 34.6 times higher than that of pure ZnIn2S4. Efficient charge separation can be attributed to the significantly enhanced photocatalytic performance, which originates from the favorable properties of the ZnIn2S4/MoS2-RGO 0D/2D heterojunction. This study provides an effective method to improve the photocatalytic performance of the ZnIn2S4 photocatalyst based on the 0D/2D heterojunction.